underscore (_) not recognized by the markdown converter

```
What steps will reproduce the problem?
1. Try to convert this a string like _From: _July 30th, 2012 _to _August 5th,
2012

2. There are spaces after the string to be emphasized: _From: _
3.

What is the expected output? What do you see instead?
we would expect this:
From: July 30th, 2012 to August 5th, 2012
instead we have the input again:
_From: _July 30th, 2012 _to _August 5th, 2012

What version of the product are you using? On what operating system?

Please provide any additional information below.

The space at the end seem to break the converter functionality

```

Original issue reported on code.google.com by `dmar...@allscenes.com` on 13 Sep 2012 at 11:22